In electrography, image charge patterns are formed on a support and are developed by treatment with an electrographic developer containing marking particles which are attracted to the charge patterns. These particles are called toner particles or, collectively, toner. Two major types of developers, dry and liquid, are employed in the development of the charge patterns.
In electrostatography, the image charge pattern, also referred to as an electrostatic latent image, is formed on an insulative surface of an electrostatographic element by any of a variety of methods. For example, the electrostatic latent image may be formed electrophotographically, by imagewise photo-induced dissipation of the strength of portions of an electrostatic field of uniform strength previously formed on the surface of an electrophotographic element comprising a photoconductive layer and an electrically conductive substrate. Alternatively, the electrostatic latent image may be formed by direct electrical formation of an electrostatic field pattern on a surface of a dielectric material.
One well-known type of electrostatographic developer comprises a dry mixture of toner particles and carrier particles. Developers of this type are employed in cascade and magnetic brush electrostatographic development processes. The toner particles and carrier particles differ triboelectrically, such that during mixing to form the developer, the toner particles acquire a charge of one polarity and the carrier particles acquire a charge of the opposite polarity. The opposite charges cause the toner particles to cling to the carrier particles. During development, the electrostatic forces of the latent image, sometimes in combination with an additional applied field, attract the toner particles. The toner particles are pulled away from the carrier particles and become electrostatically attached, in imagewise relation, to the latent image bearing surface. The resultant toner image can then be fixed, by application of heat or other known methods, depending upon the nature of the toner image and the surface, or can be transferred to another surface and then fixed.
Toner particles often include charge control agents, which, desirably, provide high uniform net electrical charge to toner particles without reducing the adhesion of the toner to paper or other medium. Many types of positive charge control agents, materials which impart a positive charge to toner particles in a developer, have been used and are described in the published patent literature. In contrast, few negative charge control agents, materials which impart a negative charge to toner particles in a developer, are known.
Prior negative charge control agents have a variety of shortcomings. Many charge control agents are dark colored and cannot be readily used with pigmented toners, such as cyan, magenta, yellow, red, blue, and green. Some are highly toxic or produce highly toxic by-products. Some are highly sensitive to environmental conditions such as humidity. Some exhibit high throw-off or adverse triboelectric properties in some uses. Use of charge control agents requires a balancing of shortcomings and desired characteristics to meet a particular situation. There is thus a continuing need for negative charge control agents which have improved properties.
U.S. Pat. No. 4,480,021 teaches the use as negative charge control agents of sulfonamides and sulfones having the formula: R.sub.1 --SO.sub.2 --R.sub.2 or R.sub.3 --SO.sub.2 --NH--R.sub.4, in which R.sub.1 is alkyl having from about 6 to about 22 carbons or aryl, R.sub.2 is aryl having from about 6 to about 18 carbons, R.sub.3 is aryl or alkyl group, and R.sub.4 is alkyl, independent from R.sub.3 having from about 6 to 22 carbons or aryl. Specific examples of aryl alkyl sulfonamides were named: para-tolyl stearyl sulfonamide, para-tolyl cetyl sulfonamide, para-xylyl stearyl sulfonamide, para-tolyl myristyl sulfonamide, and isopropyl biphenyl stearyl sulfonamide.
U.S. Pat. No. 4,464,452 teaches toner compositions including a negative charge control agent having the general structure: ##STR3## in which R and R.sub.1 are selected from H, alkyl, halo, nitro, "and the like". This patent also teaches as specific examples of negative charge control agents: di-tolyl sulfonimide, phenyl tolyl sulfonimide, diphenyl sulfonimide, di-1-naphthyl sulfonimide, hexadecyl tolyl sulfonimide, methyl tolyl sulfonimide, and dihexadecyl sulfonimide.
U.S. Pat. No. 3,577,345 teaches toners and developers including a material having the general structure: ##STR4## in which R is selected from H, Cl, Br, aryl, alkyl having from 1 to 6 carbons; R' and R" are selected from H, aryl having from 1 to 12 carbons and alkyl having from 1 to 12 carbons and chlorinated Ph-(Ph).sub.n -Ph (n=0-3). This material is not used as a charge control agent, but rather as an additive for modifying toner melt and viscosity. Similar melt and viscosity modifying additives are taught in U.S. Pat. Nos. 3,893,934 and 4,002,776. Those additives have the general structure: ##STR5## in which one of R.sub.1 and R.sub.2 is CH.sub.3 and the other is H. These three patents do not teach or suggest whether these materials are capable of functioning as charge control agents for modification of charge. Charge control agents are commonly used in the range of about 0.5 to 3.0 weight percent. The melt and viscosity additives, in these patents have concentrations in toners in the range of about 10 to 40 weight percent.
U.S. Pat. No. 5,186,736 to Ong et al teaches toners having charge control additives having the general structure ##STR6## where A and B are independently selected from hydrogen, alkyl, alkoxy, carboxy, nitro, and halogen and X and Y are independently selected from hydrogen, hydroxy, alkyl, alkoxy, carboxy, nitro, and halogen and y is 0 or 1.
U.S. Pat. No. 5,186,736 to Ort et al teaches heterocyclic N-acylsulfonamide herbicides or growth regulators having the general structure: ##STR7## where R.sup.1 is H or an aliphatic radical; R.sup.2 and R.sup.3 are H, alkyl or phenyl; W is O, S, NR.sup.4 or NOR.sup.4 ; X is CHR.sup.2, O or NR.sup.4 ; L is a (substituted) phenyl, naphthyl, or monocyclic heteroaryl radical; A is a (substituted) pyrimidyl, triazinyl, triazolyl or bicyclic heteroaryl radical; R.sup.4 is H, C.sub.1 -C.sub.3 -alkyl, C.sub.1 -C.sub.3 -haloalkyl, or phenyl; and m and n are 0 or 1.